During a freeze-drying process in a freeze dryer the product parameters (in particular the temperature of the drying good in a drying vessel) are an important process parameter. As an example, the temperature of the drying good provides information about the progress of the sublimation process and the drying process of the drying good and the temperature of the drying good can be considered for determining an end of the main drying process and for process control. General information about the process sequence during freeze-drying, about the freeze dryers addressed here and the way the product parameters of the drying good change during the freeze-drying process can be taken from the website www.martinchrist.de.
DE 10 2006 019 641 A1 proposes to sense the temperature of a drying good in a drying vessel via a freeze-dryer product sensor. The freeze-dryer product sensor comprises a sleeve made of metal, glass or ceramics. A measurement transducer arranged in the drying good extends from one end of the sleeve while an antenna extends from the other end of the sleeve. The measurement transducer is connected to the antenna via a circuit board. The freeze-dryer product sensor does not comprise any integrated power supply. Instead, power is supplied via an oscillating circuit of the circuit board, which is excited for executing oscillations in a contact-free way. The resulting oscillation of the oscillating circuit (in particular the frequency of the oscillation) depends on the temperature of the measurement transducer (and so depends on the temperature of the drying good in which the freeze-dryer product sensor is arranged). In a contact-free way, the freeze-dryer product sensor transmits a measurement signal which correlates with the oscillation. The contact-free excitation of the oscillating circuit on the one hand as well as the contact-free transmission of the measurement signal on the other hand are provided by a radio signal transmitted from the antenna of the freeze-dryer product sensor to an antenna arranged within the housing of the freeze dryer. The antenna arranged within the housing of the freeze dryer is connected to a control device arranged outside the housing via a vacuum-sealed feedthrough through the housing. In addition to the measurement signal for the temperature, the freeze-dryer product sensor also transmits sensor identification data and calibration data. In the control device, data sets for the freeze-dryer product sensor have to be provided, which in addition to the current temperature also describes the position of the drying vessel within the housing as well as the measuring object. The measurement signals of the freeze-dryer product sensor can be sampled cyclically by the control device and can be documented as a function of time. By use of a freeze-dryer product sensor of this type it is intended to sense the temperature in a drying vessel, the temperature of a supporting surface, the temperature of an ice condensator of the freeze dryer and/or a temperature in an inlet or outlet of a heating or cooling medium of the freeze dryer. DE 10 2006 019 641 A1 additionally proposes to sense a pressure signal in a corresponding contact-free way. Preferably, due to the contact-free transmission of the signals any wiring within the housing of the freeze dryer and/or of plug connections are no longer required. A shielded realization of the housing of the freeze dryer is also possible. In order to provide an interference-free data exchange between the antennas of the freeze-dryer product sensors and the antenna connected to the control device, DE 10 2006 019 641 A1 proposes to arrange the supporting surfaces of the freeze dryer during the freeze-drying process with a distance from each other which is dimensioned corresponding to the wavelengths of the frequency range used for the wireless transmission. For improving the chemical resistance and/or for reasons of hygiene, the freeze-dryer product sensors can be arranged in the sleeve made of an inert material (e.g. stainless steel, glass, plastic or ceramics). It is also possible that a transducer in a corresponding way senses residual humidity, an electric resistance or a pressure in the drying good and transmits the same in a contact-free way.
DE 20 2009 009 107 U1 discloses a bus system that, in a vacuum-sealed way, is fed through a wall feedthrough of a housing of the freeze dryer from the outside. Bus modules are connected to the bus system in parallel connection or series connection. The bus modules are connected to supporting surfaces, transducers for sensing the temperatures of supporting surfaces, transducers for sensing the electrical resistance of the drying good and/or transducers for sensing the temperatures of the drying good as well as auxiliary parts such as a valve and a ventilating construction unit. The bus system serves for power supply and bi-directional transmission of any information such as measurement data and control data. By means of the bus system it is possible to address the components connected to the bus modules individually and in this way to control them.
WO 2016/123062 A1 discloses a freeze-dryer product sensor for measuring a temperature and a humidity. In the publication, known freeze-dryer product sensors based on wire-based thermocouplers are criticized in that they require a high effort during installation, are prone to errors and might lead to a loss of the drying product in which the freeze-dryer product sensor is arranged. Furthermore, known freeze-dryer product sensors wherein the measuring principle is based on a wireless, induction-based excitation of a resonance frequency depending on the temperature of the drying product are criticized in that when using a plurality of such freeze-dryer product sensors of this type there might be an undesired interaction of the freeze-dryer product sensors. On this background the publication proposes a freeze-dryer product sensor having a plurality of measurement positions where it is possible to measure the temperature and the humidity, the plurality of measurement positions being arranged in an array of the freeze-dryer product sensor in such a way that the measurement positions can be arranged at different heights of the drying product in a drying vessel. A transmission of the measurement signals of the freeze-dryer product sensor is provided by a wireless digital communication link. The freeze-dryer product sensor comprises a supporting structure, which can be arranged in an opening of a vial and held there, as well as a sample body at which the measurement positions are arranged at positions distributed in a longitudinal direction. Furthermore, the freeze-dryer product sensor may comprise a control unit held at the supporting structure and connected to the measurement positions. The measurement positions may comprise ceramic capacitors. The measurement positions may have an extension of 2 mm so that along a measurement line six measurement positions of this type can be arranged over a height of 12 mm. It is also possible for the measurement positions to be integral components of a printed circuit board. Calibration factors for the freeze-dryer product sensors may be stored in the control unit of the freeze-dryer product sensor. For an alternative embodiment it is proposed that the calibration factors for a freeze-dryer product sensor may be stored in a database together with an associated identification code. An access to the database is possible from a processing unit arranged outside the drying chamber. The freeze-dryer product sensor uses a specific identification code in order to identify itself at the processing unit. During the loading of the drying vessels onto the supporting surfaces of the drying chamber, the locations at which the freeze-dryer product sensors are arranged in the drying chamber are determined and archived in table form. In an automatic loading system it is possible to track the vials with the freeze-dryer product sensors arranged therein to the respective position on the supporting surface of the drying chamber. When the measurement signals from the freeze-dryer product sensors are received, the specific identification code is correlated to the position of the identified freeze-dryer product sensor in the drying chamber on the basis of the allocation of the position in table form. In this way it is intended to make possible a “mapping” of the measurement signals received for a drying good for process control and process analysis. It is possible to use “USB ANT” (registered trademark) plugging modules for transmitting measurement signals, which comprise an integrated antenna as well as software for data recording and for control of the data transmission. The freeze-dryer product sensor is wirelessly supplied with power by a transmitter arranged in the drying chamber which transmits a high frequency excitation signal. It is also possible that a plurality of antennas is arranged in the drying chamber for transmitting high frequency signals in order to provide direct and short transmission paths for the high frequency signal. The positions for the arrangement of the vials equipped with the freeze-dryer product sensors can be selected on the basis of data measured before or on the basis of the qualitative characteristics of the drying chamber. The measurement signals at the measurement positions of a freeze-dryer product sensor are transmitted together with the specific identification code of the freeze-dryer product sensor. Based on the measured temperature and humidity, it is possible to control a stream of a heating or cooling fluid into the supporting surfaces or to individual parts of the supporting surfaces. Based on the plurality of measurement positions arranged at different heights in the drying good it is possible to sense the progress of the sublimation front in the drying good during the freeze-drying process, which can then be considered in the process control.
WO 2016/123177 A1 discloses the constructive design of a freeze-dryer product sensor comprising a plurality of measurement positions and measurement principles that can be used in this context.
US 2008/0272131 A1, which is not of the generic kind, relates to a high-volume thermally insulated container in which temperature-sensitive products such as pharmaceutical products, food products, chemical products or biological products are stored or contained during processing, distribution, storage, transport and shipping and are held at a low temperature due to the thermal insulation. A monitoring device serves for monitoring the temperature in the container. The monitoring device comprises an RF transponder, in which way wireless temperature measurement is intended to be enabled without the need to provide an opening of the container. The RF container comprises an RF antenna, a temperature sensor, a battery and an electric circuit. A memory component is intended to enable storage of at least one measurement of the temperature, e.g. a temperature pattern over time. The container is intended for storage of the mentioned products at temperatures below −70° C. or even below −80° C. In order to keep up temperatures below −70° C., the products are arranged in a refrigerant, which may be dry ice. In temperature ranges like that, the battery of the monitoring device may fail, since an electrolyte of the battery may freeze even at a temperature below −30° C. The document suggests arranging the temperature-sensitive battery in a region of the wall of the container, in which the battery due to the temperature rise between the inner side of the wall and the outer side of the wall is exposed to a higher temperature at which the electrolyte of the battery cannot freeze yet. In order to insulate the wall, a polymeric foam (especially with polyurethane, polystyrene, polyolefin or a combination of the mentioned materials) may be used. It is also possible for the wall to be comprised of vacuum isolated panels (VIPs). It is furthermore possible for insulation to be provided by metallic foil layers. The monitoring device may have further functions, such as identifying, monitoring and/or tracking. In addition to the mentioned components, electronic components such as e.g. processors, memory components, external interface components (wired or wireless), sensor elements, display elements such as, e.g., an LCD display, power supplies, transistors, diodes, passive components such as resistors, capacitors and inductors, smart tags, smart cards, RF tags, RFID tags, wireless tags, data loggers and similar may be integrated into the monitoring device. The monitoring device may, additionally, also measure a relative humidity, a light intensity, a voltage, a pressure or vibrations in the container. The monitoring device may be activated by manual actuation of a switch or in a wired or wireless way, e.g. by means of an additional RFID reader.
Further prior art is known from WO 2009/030760 A1 and US 2006/239331 A1.